1. Field of the Invention
The present invention relates to a technique intended to prevent illegal copying of information signals supplied, for example, from recording media or via networks.
2. Description of the Related Art
With increased commercialization of VTRs (Video Tape Recorders), digital VTRs, and reproducing or recording/reproducing apparatus for DVDs (Digital Video Discs), a large amount of software capable of being reproduced by those apparatus have been provided. Also, with the expanding use of networks such as the Internet, users can also obtain a variety of software via these networks.
On the other hand, there is a concern that marketed software may be copied without limitations, thus allowing users to steal the software. To cope with this problem, it has been proposed to add copy control information to main information signals such as video signals. This copy control information includes, e.g., prohibition of copy, permission of copy, or limitation of copy generation. Copy control is performed in accordance with the added copy control information. In the case where main information signals are digital signals and are supplied from discs such as DVDs or via networks, additive information such as copy control information is recorded in an area spatially distinct from the main digital information signals, for example, in a header included for each block of the digital information signals. Also, where main information signals are analog video signals, an additive information signal, such as copy control information, is superimposed in an unused horizontal zone within a vertical blanking period of the analog video signals so that the analog video signals will not be affected.
A recording apparatus for receiving main information signals such as analog video signals and recording the received signals on a recording medium is constructed, by way of example, as shown in FIG. 10. The recording apparatus includes a copy control information detector 53 and a copy permission/prohibition controller 54. Copy control information detector 53 extracts copy control information that was added to the supplied information signals as mentioned above. Based on the copy control information extracted by copy control information detector 53, copy permission/prohibition controller 54 controls a writer 52 to write permission or prohibition signals when recording the main information signals.
As described above, copy control information is added to an indirect portion, e.g., a header of digital information signals or an unused horizontal zone within a vertical blanking period of the analog video signals. Therefore, the copy control information is relatively easily removed from the signal by filtering or tampering with the signal, resulting in disabling the copy control.
Main information signals, once illegally copied after the copy control information has been tampered with, can be freely reproduced and output after this illegal copying. In other words, the main information signals thus output can be further illegally copied over and over again on additional recording media. The illegal copying can therefore be repeated without limitation. Users or purchasers of illegal copies cannot discern whether main information signals such as video signals have been illegally copied. Accordingly, even if main information signals have been illegally copied, complaints are not voiced to dealers who are illegally copying and selling the information signals, because the users suffer from no disadvantages so long as they can utilize the copied information signals without problems. Such a situation has been one of the reasons that illegal copying of information signals has continued.